The present invention relates to a method for a wireless communication system, and more particularly, to a method of adjusting modulation and coding scheme (MCS) in a wireless communication system.
In IEEE 802.11 wireless systems, channel sounding and feedback process is commonly used for channel estimation. In multiple-input and multiple-output (MIMO) systems, each channel sounding and feedback process is followed by a series of MIMO frame exchange. During channel sounding and feedback, a transmitting device (initiator) sends a sounding announcement (e.g., null data packet announcement (NDPA)) followed by a sounding packet (e.g., null data packet (NPD)) to a receiving device (responder) participating in the process. The responder estimates the channel during the preamble portion of the sounding packet. The responder then feedbacks the average signal-to-noise ratio (SNR) and channel state information (CSI) to allow the initiator to compute the transmit antenna weights (precoding) for MIMO transmission. Feedback packet may also include other channel quality metrics such as MCS, BER, SNR/SINR, and mutual information.
Feedback of accurate channel quality information such as SNR and MCS allows the transmitter to make correct decision regarding transmission bandwidth adjustment as well as MCS adaptation to improve system performance. However, the MCS selected according to the feedback channel quality information may be outdated because the channel quality varies with time. The throughput performance of the wireless communication system may be degraded because of the time varying channel quality. Thus, how to adjust the MCS adopted by the wireless communication system becomes a topic to be discussed.